MEXICO CITY (Reuters) -- A cluster of mysterious objects that surrounded a Mexican Air Force plane, alarming the pilots and sparking a UFO scare, could be a weather phenomenon known as ball lightning, a scientist said on Friday.

The pilots grew nervous during a routine drugs surveillance flight in March when their radar detected strange objects flying nearby and an infrared camera showed 11 blobs of light, invisible to the eye, hovering or darting about their plane.

Mexico's Air Force this week released footage from the infrared camera that was shown widely on television.

As Mexican and international media published photographs of the objects, UFO Web sites saw the case as possible evidence of a new sighting of some form of extraterrestrial life.

But nuclear science researcher Julio Herrera said the blobs of light may have been nothing more than ball lightning -- glowing spheres that are little understood but often sighted near the ground during thunderstorms.

"Just as you have lightning between clouds and ground, you can also have it within the clouds and sometimes ball lightning can develop. I feel this is one of these rare events," said Herrera, based at Mexico's National Autonomous University.

"It's a very rare atmospheric phenomenon and it would be very interesting to be able to analyze all the information these pilots obtained," he told Reuters.

UFO follower Jaime Maussan said on Tuesday the objects seemed "intelligent" after they turned around to surround the plane chasing them -- but Herrera said electrical discharges in ball lightning could have been attracted to the plane as a conductor.

_________________________
Those who say do not know.Those who know do not say.